Technical Abstract:
Background: One-hundred eight cases of E. coli O157:H7 infection occurred in association with the 2004 North Carolina State Fair. Fifteen children were diagnosed with hemolytic-uremic syndrome. Molecular subtyping by pulsed-field gel electrophoresis (PFGE) identified an indistinguishable outbreak pattern, designated Pattern A, which was predominant among human clinical isolates. Environmental sampling of the fairgrounds was conducted to support the outbreak investigation. Methods: Composite ground samples (shavings, manure, and soil) and surface swab samples from structures were taken in ten distinct animal areas. Swab samples from a cider press and water fountain were also taken. In addition to composite ground samples and surface swabs, flies were netted. Culture-positive areas were systematically re-sampled. Additionally, swabs from a case-patient's stroller and from a well child's shoe were cultured. Sensitive culture methods, including selective broth enrichment, immunomagnetic separation, and plating on selective media, were used. Isolates were subtyped using PFGE. Results: Eighteen (15%) of 122 environmental samples yielded E. coli O157:H7, including one fly pool. All positive environmental samples were from animal areas. Multiple PFGE patterns were identified among the 18 isolates. Ten of 18 isolates were from the Petting Zoo B environment. Of these, eight isolates demonstrated Pattern A. Systematic resampling of soil from Petting Zoo B resulted in 19 additional Pattern A isolates primarily from an open area used to house goats and sheep. Swab samples from the stroller and child's shoe also yielded E. coli O157:H7. Conclusion: E. coli O157:H7 was isolated from multiple animal areas of the fairgrounds. Isolates from Petting Zoo B were indistinguishable from predominant PFGE subtype in humans. Systematic sampling of Petting Zoo B found that the soil was uniformly contaminated where the goats and sheep were in direct contact with the public. Environmental sampling, coupled with sensitive culture methods and molecular subtyping, supported the implication of Petting Zoo B as the location where transmission occurred.